Extra non-functional preview process are launched

• I open a pdf preview.
• Then I open an html preview for the same file.
• It replaces the first pane but two preview terminals are active now.
• Even if I change the port number in the URL of the preview pane or press the back arrow, I'm unable to return to the pdf view.

This also goes the other way around, if I first had the html preview open and wanted to preview the pdf rendering.

As in https://github.com/quarto-dev/quarto/issues/371 there is a disconnection between terminals and preview panes, here made worse because there are two active terminals.

But in this case there is also a bug since I'm able to see running pdflatex in both preview terminals, as if i Quarto launched the latex engine twice, one in the preexistent terminal and the other in a new one. Often the preview pane gets empty and one of the underlying processes abort with an error:

https://github.com/quarto-dev/quarto/assets/2845433/dbe646c0-e4bb-4ac2-9162-12ed6a84e6c0

No source file or test is named. Reproduce the PDF-to-HTML and HTML-to-PDF preview switches while watching both preview terminals, then trace the preview-pane and process lifecycle; done means switching previews leaves only the intended process active and restores the selected rendering reliably.